1. Field of the Invention
The invention relates to a lamp string, more particularly to a lamp string including bulb mounting units, each of which has parts with orienting means.
2. Description of the Related Art
In a festival or an occasion for presenting 1 a cheerful atmosphere, such as Christmas, a lamp string, especially one with many colored bulbs, is wound on an object to be decorated, such as a Christmas tree, for providing illumination during the night.
As shown in FIGS. 1, 2 and 3, a conventional decorative lamp string 1 includes a plurality of bulb units 2 arranged electrically in series with each other so as to form an electric current loop, and a plug 3 coupled electrically to the bulb units 2 and adapted for plugging into a power source. Each of the bulb units 2 includes a receptacle 21, a mounting seat 22 mounted in the receptacle 21, and a light-emitting diode 23 mounted on the mounting seat 22. The receptacle 21 provides a cathode conductive contact 211 and an anode conductive contact 212. The light-emitting diode 23 includes a cathode conductive lead 231 and an anode conductive lead 232. When the light-emitting diode 23 is mounted on the mounting seat 22, the cathode conductive lead 231 and the anode conductive lead 232 must be coupled electrically to the cathode conductive contact 211 and the anode conductive contact 212, respectively, so as to establish the electric current loop and so as to permit activation of the light-emitting diodes 23. To prevent the mounting seat 22 from being inserted in an incorrect orientation, the mounting seat 22 includes a pair of spaced apart triangular protrusions 221 extending radially from a housing thereof, and the receptacle 21 is formed with a pair of triangular grooves 213 conforming to the triangular protrusions 221, such that, when the mounting seat 22 is inserted into the receptacle 21, the triangular protrusions 221 must be aligned with the triangular grooves 213 so as to enable the triangular protrusions 221 to be fully extended into the triangular grooves 213.
However, since the mounting seat 22 is made of plastic material, forced insertion of the triangular protrusions 221 of the mounting seat 22 into the triangular grooves 213 of the receptacle 21 in an incorrect orientation can still happen, thereby damaging the structures of the mounting seat 22 and the receptacle 21, and thereby resulting in wrong polarity for the light emitting diodes 23.